Numbers

In General

The following guidelines apply to the majority of CU Boulder writing except for scientific, statistical, technical and mathematical writing.

Spell out one to nine, use figures for 10 and above

  • The Alumni Association recognized 10 people at the awards ceremony, including two alumni who have demonstrated extraordinary service to CU Boulder.

Exceptions: Always use figures for headlines, percentages, decimals, credit hours, GPAs, book sections and pages, ages, distances and dimensions, quantities combining whole numbers and fractions, and when symbols rather than abbreviations are used for units of measure.

Use the percent  sign (%) in formal running text and in tables, charts, scientific and statistical copyÌý²¹²Ô»å some informal and promotional copy.

  • We printed the first draft on 8.5" x 11" paper.
  • In his first semester, when he carried 9 credit hours, he earned a 3.1 GPA while spending 30% of his time on a work-study job.
  • You’ll find the answer in Chapter 2 on Page 31.
  • Her brother gave $5 to the CU Foundation.
  • Her sister gave $1 million to the CU Foundation.
  • He is 5 years old.
  • She walked 5 miles.
  • He is 6 feet 2 inches tall.

Spelling out large round numbers is preferred.

  • She gave the museum more than two hundred thousand artifacts.

Use a combination of figures and words with numbers in the millions and larger.

  • The population increased by 2.3 million.

Use a comma for numbers with more than three digits unless they represent SAT scores or years.

  • In-state tuition for 2024–24 was $14,002 per year.
  • The book, which was published in 2010, has 1,229 pages.
  • His combined SAT score was 1235.

Spell out numbers at the beginning of a sentence or rephrase the sentence to avoid beginning with a number.

  • Forty-nine students received the new degree at the May commencement.

Dates

The U.S. preference is for styling dates as month, day and year. Do not use ordinal numbers in dates. When listing a month, day and year, set off the year with commas. When listing only a month and a year, do not separate the year with commas.

  • Spring commencement will be held May 8, 2025. (Not: 8 May 2025)
  • The new policy goes into effect March 10, 2025, with approval from the board.
  • The awards were announced in April 2024.

Fractions

Spell out fractions less than 1, using hyphens between the words.

  • Two-thirds of the class was late.
  • A four-fifths majority voted in favor of the amendment.

Grades

Spell out grades lower than 10, use numerals for grades 10 and above. Do not hyphenate as an adjective.

  • Maria teaches second grade.
  • The 10th graders were moved to the ninth grade classroom.

Inclusive Numbers

When dealing with ranges of numbers (such as page numbers and years), carry over all the digits that change and include at least two digits for the second number. Use an en dash rather than a hyphen between the numbers.

  • Pages 1,004–05
  • 2024–25
  • 1999–2009

Unless the century changes, inclusive years should be styled with only the last two digits of the second number (1999–2009, but 2024–25). Inclusive years on publication covers, however, can be styled with all four digits of the second number (2024–2025 versus 2024–25) at the designer’s discretion.

Note that in running text, the en dash is not an acceptable substitute for the word ³Ù´ÇÌýunless the numbers are in parentheses.

  • She taught anthropology from 1952 to 1992.
  • She taught anthropology at CU (1952–60), Harvard (1960–88) and Berkeley (1988–92).

Metric Measures

If you are writing for an international audience (for example, writing a brochure to recruit international students for a new program or publicizing an international conference), include metric measurements.

  • The CU Boulder Main Campus averages 5,400 feet (1,645 meters) in altitude. The average Boulder daytime high temperature in July is 88 F (31 C).

Monetary Units

  • The fee is $4.
  • I gave her 5 cents.
  • The renovation project will cost $1 million.

Ordinal Numbers

Spell out ordinal numbers from first to ninth.

  • She placed fourth out of 525 competitors.
  • The 21st century was fodder for many imaginative novelists and entrepreneurial visionaries during the latter half of the 20th century.
  • Hyphenate as an adjective: She is an expert in 17th-century Chinese pottery.

Room Numbers

Capitalize room when used with a number. Campus room numbers should be referred to with the name of the building and the room number, in that order, with the room number set off in commas.

  • The Office of the Registrar is located in Regent Hall, Room 105.

In a Series

Apply the standard guidelines.

  • She has 10 nieces, six nephews and 15 cousins.

Telephone Numbers

Do not put the area code in parentheses and use hyphens, not periods: 303-735-1079.

Time

Use figures with a.m. or p.m. (lowercase) to indicate specific times. Use noonÌý²¹²Ô»åÌý³¾¾±»å²Ô¾±²µ³ó³Ù in place of 12 p.m. and 12 a.m., respectively, for clarity.

  • The lecture will begin at 2 p.m.
  • The meeting starts at 8:30 a.m.
  • The conference will take from 9 to 11 a.m.

Years

Use an s without an apostrophe to indicate spans of decades or centuries.

  • The 1800s
  • The ’80s (note the direction of the apostrophe; not the '80s)

Use the correct placement for A.D. and B.C. (all caps).

  • Hannibal died in 183 B.C.
  • King George IV died in A.D. 1830.